Correlated polarization-switching kinetics in bulk polycrystalline ferroelectrics. II. Impact of crystalline phase symmetries

Electric depolarization fields have a great impact on the polarization-switching kinetics in ferroelectrics although they are often neglected in statistical considerations. Analysis of statistical distributions and correlations of polarization and electric field during the field-driven polarization reversal in a bulk polycrystalline ferroelectric by means of the two-dimensional self-consistent mesoscopic switching (SMS) model has revealed that correlations, mediated by electrostatic fields, are mostly isotropic and short range at a typical scale of the mean grain size [Phys. Rev. B 96, 054113 (2017)]. However, the magnitude of emerging depolarization fields remains substantial and strongly influences the switching kinetics. It is known, on the other hand, that the effect of inhomogeneities, such as a granular structure, on the electric field pattern and local field magnitudes is considerably overestimated in two-dimensional simulations. Three-dimensional extension of the SMS model in the current study allows a realistic evaluation of the impact of spatial correlations on the polarization switching in ferroelectric ceramics and opens a possibility to consider materials of different phase symmetries. It is shown that bound charges at grain boundaries due to mismatching grain polarizations as well as the subsequent depolarization fields are essentially dependent on the crystalline symmetry. This explains great differences in statistical field distributions and polarization kinetics observed in ceramics of different phase symmetries. Field correlations are anisotropic, depend on the material symmetry, but remain in all cases short range at the scale of a grain size. This sheds light on the success of models assuming statistically independent switching of different regions. Evolution of the statistical field distributions in the course of polarization reversal is also symmetry dependent but temporal changes in distributions are not substantial which clarifies a good performance of models neglecting the feedback via depolarization fields.